The NAND-type flash memory is one type of nonvolatile semiconductor memory device. The write operation in the NAND-type flash memory is carried out as follows.
After loading the data from external sources, the program that writes the data in the memory cell and verification for verifying whether the data is correctly written or not, are carried out. Then, verification and program are repeatedly carried out until there is a confirmation that the data is correctly written in the memory cell by verification.
If upon verification, it is confirmed that the data is not correctly written, the write voltage Vpgm will be slightly increased, and the verification will be carried out again. In this manner, the write operation is carried out.